For example, separation membrane modules used for seawater desalination, ultrapure water production etc., are conventionally known. For example, Patent Literature 1 discloses a separation membrane module 10 as shown in FIG. 12 and FIG. 13. The separation membrane module 10 includes a tubular pressure container 11 and a plurality of separation membrane elements 12 inserted in the pressure container 11 in a line. As shown by an arrow in FIG. 12, when raw water is supplied into the pressure container 11 from one end of the separation membrane module 10, the raw water is separated into permeated water and concentrated water by separation membranes of the separation membrane elements 12, and the permeated water and the concentrated water are separately discharged from the other end of the separation membrane module 10.
Each separation membrane element 12 has a layered body including a separation membrane and wound around a central pipe, and has a pair of end members 13 disposed in such a way as to sandwich the layered body. In the separation membrane module 10 shown in FIG. 12 and FIG. 13, a packing 15 having an approximately U-shaped cross-section is mounted on the end member 13 located on the upstream side, and the packing 15 seals a gap between the separation membrane element 12 and the inner circumferential face of the pressure container 11 by means of a pressure of the raw water applied from the upstream side.
The packing 15 has an outer diameter which is nearly equal to the diameter of the inner circumferential face of the pressure container 1, even in a natural posture where no pressure from the upstream side is exerted. Therefore, when the separation membrane element 12 is inserted into the pressure container 11, the separation membrane element 12 is conventionally pushed into the pressure container 11 in such a manner that the packing 15 pressed by the weight of the separation membrane element 12 is rubbed against the inner circumferential face of the pressure container 11.